Conventionally known flush water tank apparatuses for storing flush water for flushing a toilet furnished with a discharge apparatus have included those such as Japanese Patent Unexamined Publication S61-72144 (Patent Citation 1), wherein as a flush water tank apparatus for storing flush water used to clean a toilet, an opening is formed on the side surface of a cylindrical body disposed to surround a discharge port formed at the bottom portion of a reservoir tank, and a valve body capable of opening and closing that opening is provided, so that for large flushes, the flush water volume is increased by allowing the opening on the cylindrical body to stay open, whereas for small flushes, the flush water volume is reduced by closing the cylindrical body opening with the valve body, so that flushing can be switched between the two stages of large and small flush.
In the discharge apparatus disclosed in Patent Citation 1, a reservoir cylinder is provided on the inside of the cylindrical body; a float capable of up-and-down motion in tandem with the valve body for closing the discharge port is disposed inside this reservoir cylinder, and by forming a small discharge pathway in the reservoir cylinder, discharge of flush water from the small discharge pathway in the reservoir cylinder can be started when discharge starts, gradually lowering the water level in the reservoir cylinder, while the discharge valve body drops together with the drop of the float as that water level falls, and the discharge port is closed by the valve at the desired timing.
Further disclosed in Japanese Patent Unexamined Publication 2002-21144 (Patent Citation 2) as a flush water tanks apparatus for storing flush water for cleaning a toilet, is an apparatus furnished with a discharge apparatus, whereby a discharge port formed at the bottom portion of the reservoir tank is opened and closed by a float valve, multiple water passage holes are formed in the side surface of a cylindrical body disposed to surround that discharge port, and the opening cross sectional area of those water passage holes is adjusted to regulate the volume of flush water supplied to the toilet.